How are you doing it...usercontrol with a RadWindow, or just dragging the widget onto the page?
So I assume you defined
the behaviors? If you can get at the .show function that means you can also get at the set_behaviors client event (should be able to anyway) LINK
...there should be no problem assuming you can get a clientside $find reference to the object.
Personally I don't like using the built-in widgets, they're just the normal controls, almost useless without some code behind...not sure why most are there without custom designers.